The discussion of the background of the invention herein is included to explain the context of the invention. This is not to be taken as an admission that any of the material referred to was published, known or part of the common general knowledge at the priority date of any of the claims.
An optical lens is typically made of plastic or glass material and generally has two opposite surfaces which co-operate with one another to provide a required corrective prescription. When the positioning or shape of one of these surfaces with respect to the other is inaccurate, optical errors can be created.
Manufacturing of an optical lens to the required prescription requirements typically includes machining the surface of a semi-finished lens or lens blank. Typically, a semi-finished lens has a finished surface, for example the front surface and an unfinished surface, for example the back surface. By machining the back surface (also named “rear surface”) of the lens to remove material, the required shape and positioning of the back surface with respect to the front surface for the desired corrective prescription can be generated.
Optical lenses, and in particular ophthalmic lenses, require very high quality manufacturing process in order to obtain high quality optical lenses.
Controlling the quality of the produced lenses is a complex task.
One solution consists in measuring the surface that has been manufactured to try to compare such surface with the nominal surface to be manufactured.
Such solution presents some drawbacks.
First, such solution considers the manufactured surface whereas the quality of an ophthalmic lens is better quantified by the optical function of the ophthalmic lens.
Secondly, not only the shape of the manufactured surface but also the position of the manufactured surface with respect to the opposite surface of the ophthalmic lens has a strong impact on the overall optical quality of the ophthalmic lens. Being able to determine the position and shape of the manufactured surface is not straightforward from the measurements of such manufactured surface.
Another solution consists in measuring the full optical function of each manufactured optical lens. Such solution is very time consuming and therefore expensive because it involves dedicated measurement tools and setups.